Conventionally, aluminum has been the main wiring material in the processing of semiconductor wafers. Recently, in order to increase the degree of integration of wiring, an increase in the signal delay time has been prevented by switching aluminum to copper, which has a high electrical conductivity. The damascene method is used for the formation of copper wiring. Generally in the process, a wiring pattern is formed on a silicon wafer, after which a barrier layer or seed layer is formed by a sputtering or CVD method, a wiring pattern is embedded by electroplating, and the excess deposited copper is removed by CMP. As wiring patterns have become increasingly finer, the coverage of copper seed layers on the inside walls of vias and trenches formed by sputtering methods has become inadequate, thus causing the defects at the electroplating. A method for solving this problem has been researched.
Electroless plating is one method of forming a metal coating film on an underlying material that does not possess conductivity; this technique is utilized in the formation of printed wiring on resin substrates and the like. A method known as activation, in which a noble metal such as palladium or the like is adhered to the underlying material beforehand as a catalyst, is common pre-treatment for a semiconductor device in such electroless plating. In the past, methods have been used in which Pd is adhered by an immersion treatment in an aqueous solution of PdCl2 following treatment with a hydrochloric acid aqueous solution of SnCl2, or in which Pd is supported on the surface by means of a colloidal solution containing Sn and Pd.